Biology of FUNgi
Lecture 07
Deuteromycetes - the mitosporic
fungi
A look back...
• What are Archiascomycetes?
• What are Saccharomycetales?
• What separated the primitive ascomycetes from the
filamentous ascomycetes?
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Fungus of the day Penicillium chrysogenum
Taxonomy: Phylum (subphylum) Ascomycota
Order - Eurotiales (anamorphic)
Family - Trichocomaceae
Today we will share one of the greatest success
stories of a sloppy microbiologist. We will be
introduced to the discovery and production of
penicillin by Penicillium chrysogenum.
It is a fungus on a dish.
Penicillium chrysogenum
A typical conidial synnema
of Penicillium
Fungus of the day Penicillium chrysogenum
This is also a wonderful story in history of
microbiology or mycology. Sir Fleming returned
from a vacation to his Staphylocuccus cultures in
1928. The cultures were contaminated with
Penicillium notatum. He isolated the culprit which
kept his bacteria from growing.
Sir Alexander Fleming
Using this culture, group of scientists were able to
establish first culturing facility to produce enough
penicillin to start experimental tests on the
antibiotics.
Fleming’s contaminated
plate.
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Fungus of the day Penicillium chrysogenum
After numerous trials on different types of
culturing devices, this group in Oxford found that
best culturing conditions could be established
with hospital bedpans renamed promptly
“penicillium flasks”.
First trials of penicillin were a grand success.
Albert Alexander’s condition was greatly
improved after ca 1g of penicillin. Penicillin was
not abundant enough to save his life, it needed to
be repurified from his urine to be able to continue
treatment. He eventually died as a result of his
infection.
Bedpan cultures for penicillin
production
Fungus of the day Penicillium chrysogenum
The British may not have had enough experience in
large-scale production of fungal metabolites.
Americans were far ahead in this game; they were
using fermentors to produce citric and humic acids
already. Citric acid is used in soda, it may be that
soda came to rescue the world from infectious
diseases in this respect.
In addition to providing the system for culturing
fungi for penicillin, Mary Hunt from Peoria IL,
found the hyper-producer strain of Penicillium
chrysogenum which replaced the original P. notatum
strain. She bought the moldy cantaloupe at a local
market.
Fermentors used for
penicillin production
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Fungus of the day Penicillium chrysogenum
To exemplify the importance of penicillin, it may
have expedited the end of WWII in Europe like the
nuke did in the Pacific. Death from infections
accounted for 15% of total loss of troops in WWI,
these were nearly absent towards the end of WWII.
Needless to say, penicillin was not made available to
axis nations.
Fermentors used for
penicillin production
The point being, penicillin was the first effective
biotechnologically produced antibiotic. Prior to that
we were confined to sulfur and copper containing
chemical drugs. Aren’t fungi wonderful!
A look forward…
• Saccharomycetales…
• What are the mitosporic fungi?
• How do the mitosporic fungi relate to
meiosporic fungi?
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Phylum Ascomycota Saccharomycetales
• Saccharomyces cerevisae
pointers for the life cycle
• Asexual reproduction by
budding in both haplo- and
diplophase.
• Heterothallism exists even in
true yeasts.
• The zygote develops into an
ascus after several diploid
generations.
Generalized ascomycete
life cycle -focus on
mitosporic phases
• Filamentous ascomycetes ascogenous hyphae, ascocarp,
forcible spore discharge and
modified ascus tip to allow that
discharge.
• Also, (usually) no yeast-like phase
in their lives.
• Many have a quicker means for
dispersal - the mitotic
conidiospores.
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The deuteromycetes - imperfect
fungi
• Traditionally, the conidiospore and/or the conidiophore
structures as well as their development (conidiogenesis)
• This was called the Saccardoan system (after Saccardo
1899).
• Saccardoan system may not reflect true evolutionary
relationships - it is an artificial classification.
• Similar conidial structures may occur in different genera
and families of meiotic taxa.
Deuteromycetes - the many
shapes of conidiospores
• Helicospores - trap a bubble of air
to make them float in water.
• Staurospores - also an adaptation to
aquatic environment; pegs covered
with adhesive which will allow
attachment to woody or leaf
substrate in streams (the Ingoldian
fungi).
• Dictyo- and phragmospores - thickwalled and melanized, typical for
soil-inhabiting fungi; possibly an
adaptation to avoid predation,
desiccation or exposure to UVradiation.
Staurospores and
helicospores
Phragmospores
and dictyospores
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Deuteromycetes - the many
shapes of conidiophores Conidiophores of coelomycetes
• Coelomycetes - mitotic fungi which
produce conidiospores in protective
structures
• Hyphomycetes. Mitotic fungi whose
conidiophores are exposed.
and hyphomycetes
An acervulus and a synnema different types of conidiomata
Sexual vs. asexual stage
Aspergillus sp.
Mitotic divisions and
conidiophore differentiation –
mitospores
Mycelium - vegetative stage
Same organism –
dispersal by meiotic
vs. mitotic spores.
Anastomosis, plasmogamy,
karyogamy and meiotic
divisions – meiospores
Eurotium sp.
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Same organism – two names?
Aspergillus sp.
Mitotic divisions and
conidiophore differentiation –
mitospores
Mycelium - vegetative stage
Same organism – dispersal by
meiotic vs. mitotic spores.
Anastomosis, plasmogamy,
karyogamy and meiotic
divisions – meiospores
Eurotium sp.
Same organism – two names?
Anamorphic - asexual stage
Teleomorphic - sexual stage
Eurotium sp.
Aspergillus sp.
Eurotium
Aspergillus
Penicillium
Talaromyces
Holomorph
Eurotium
Talaromyces
Same organism – dispersal by
meiotic vs. mitotic spores.
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Same organism – two names?
Summary:
Aspergillus sp.
Anamorphic - asexual stage
Teleomorphic - sexual stage
Eurotium sp.
If both known, we talk about a holomorph:
e.g. Eurotium sp. with Aspergillus sp.
anamorph
Eurotium
Talaromyces
Holomorph
Deuteromycetes – different names for
the mitotic and meiotic stages
• Isn’t it confusing to have two
names for different organisms?
• Incentives
– Many organisms have no known
sexual (meiosporic) stage
– Many mitosporic stages are very
characteristic but may be hard to
relate to the meiosporic ones
– Easy ID in pure culture.
• Initially the plan was to transfer
mitosporic taxa to meiosporic
ones after this was discovered.
Aspergillus sp. culture and
conidiophore can be defined by their
morphological characteristics - so can
Eurotium sp.
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The deuteromycetes - imperfect
fungi
• How does one become imperfect?
– Single mutation in a long line of expressed genes which result in the
production of a fruiting body?
– Hybridization (a debated issue in fungi - evidence is accumulating)
may lead to loss. Too many tangling pairs of chromosomes interfere
with meiotic divisions?
– Loss of mating types in heterothallic fungi. If one mating type is in
more of an advantage in certain regions or substrates, other mating
types may become increasingly rare - or totally disappear from the
population. In other words, if we live under conditions that are
characterized by a strong directional selection. An example:
Ophiostoma novo-ulmi the causal agent of DED.
The deuteromycetes - imperfect
fungi
• Among the European isolates of Ophiostoma novoulmi one mating type is very rare. This is assumed
to be a result of strong directional selection in a
new environment and new host taxa. The very
reason for predominantly asexual reproduction?
• In the case of another, but similar, disease causing
agent Ophiostoma ulmi both mating types are
present at equal frequences - no directional
selection?
Elm trees (Ulmus sp.)
knocked out by Ophiostoma
novo-ulmi
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Pros and cons of mitotic stages
• Muller’s Ratchet.
• Are mitotic species static? No! Mutation happens.
Unfortunately, most mutations are deleterious.
• Does mitotic stage exclude sex? No! We just may not be
aware of it; sexual reproductive structures are infrequent
and/or minuscule - escape the mycologists’ sharp eyes.
• Recombination in absence of sex? Parasexual recombination.
What is that?
The deuteromycetes - parasexual
cycle
• Parasexual cycle refers to a situation where recombination
takes place without sexual reproduction. How does this
happen?
• Four important requirements:
– Heterokaryosis: two types of nuclei in a single mycelium anastomosis and insertion of a foreign nucleus (mother nature is a
bitch), mutations or chromosomal rearrangements.
– Karyogamy within somatic mycelium to establish stable or
unstable diploid.
– Crossing over at mitosis in the diploid nucleus.
– Haploidization - recall no meiotic division
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The deuteromycetes - parasexual
cycle
• The haploidization is likely to be acquired by aneuploidy,
the gradual loss of chromosomes, until the normal haploid
complement is restored.
• This sounds like science fiction. However, the recovery of
non-parental types in somatic cultures evidences
recombination events (zonation, changes in colony color,
antibiotic resistance, nutritional requirements, conidial
characters).
The deuteromycetes - occurrence
• Where do asexual ascomycetes the deuteromycetes occur?
• They inhabit same substrates and same habitats as their
sexual states do. Occasionally both may occur together.
• Like the ascomycetous teleomorphs, anamorphic or mitotic
ascomycetes occur in terrestrial, aquatic and marine
environments.
• Some imperfect fungi are also parasites and disease
causing agents of animals and humans...
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The deuteromycetes - imperfect
fungi
• Aspergillus sp., for example, can infect
human tissues causing mycoses or
pulmonary discomfort with
pneumonia-like symptoms
Typical Aspergillus
conidiophores
Summary...
• Asexual dispersal by mitospores
• Holomorph = meiosporic + mitosporic state
• Causes and pros/cons of mitotic states
• Parasexuality
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